Methods and apparatus for active substrate precession during chemical mechanical polishing

ABSTRACT

In some aspects, a chemical mechanical polishing (CMP) apparatus is provided that includes a polishing head having (a) a rotatable spindle; (b) a membrane coupled to the rotatable spindle and adapted to press a substrate against a polishing pad during polishing of the substrate; and (c) a retaining ring rotatable coupled to the spindle and adapted to surround a substrate being pressed against a polishing pad during polishing and to limit lateral movement of the substrate relative to the polishing head. The CMP apparatus also includes a drive mechanism coupled to the retaining ring and adapted to drive the retaining ring at a different rate of rotation than the spindle during polishing. Numerous other aspects are provided.

FIELD OF THE INVENTION

The present invention relates to semiconductor device processing, andmore particularly to active substrate precession during chemicalmechanical polishing.

BACKGROUND OF THE INVENTION

During semiconductor device manufacturing, numerous material layers aredeposited, patterned and etched to form electronic circuitry and/orelectrical connections on the substrate. In many instances, a topsurface of a substrate may be planarized between processing steps. Suchplanarization typically is performed using an etch-back step or chemicalmechanical polishing (CMP).

During CMP, a substrate is placed face down on a polishing pad andpressed against, and rotated relative to, the polishing pad via apolishing head in the presence of a slurry. The slurry may containabrasive particles and/or chemicals that assist in material removal fromthe substrate. Polishing is continued until enough material is removedto form a planar surface on the substrate.

Maintaining uniformity across a substrate during CMP is important toensure uniform layer thicknesses for devices formed on the substrate.However, maintaining thickness uniformity across the entire surface of asubstrate is difficult. This is particularly true for larger diametersubstrates. Therefore, a need exists for methods and apparatus forimproving uniformity during chemical mechanical polishing, particularlyfor large substrate sizes.

SUMMARY OF THE INVENTION

In some aspects, a chemical mechanical polishing (CMP) apparatus isprovided that includes a polishing head having (a) a rotatable spindle;(b) a membrane coupled to the rotatable spindle and adapted to press asubstrate against a polishing pad during polishing of the substrate; and(c) a retaining ring rotatable coupled to the spindle and adapted tosurround a substrate being pressed against a polishing pad duringpolishing and to limit lateral movement of the substrate relative to thepolishing head. The CMP apparatus also includes a drive mechanismcoupled to the retaining ring and adapted to drive the retaining ring ata different rate of rotation than the spindle during polishing.

In some aspects, a chemical mechanical polishing apparatus is providedthat includes a polishing head having (a) a rotatable spindle; (b) amembrane coupled to the rotatable spindle and adapted to press asubstrate against a polishing pad during polishing of the substrate; (c)a retaining ring coupled to the spindle and adapted to surround asubstrate being pressed against a polishing pad during polishing and tolimit lateral movement of the substrate relative to the polishing head;and (d) at least one rotation mechanism coupled to the retaining ring,adapted to contact a substrate during polishing and adapted to allow thesubstrate to rotate at a different rate than the spindle during theduring polishing.

In some aspects, a method of polishing a substrate is provided thatincludes pressing the substrate against a polishing pad using apolishing head having (a) a rotatable spindle; (b) a membrane coupled tothe rotatable spindle and adapted to press the substrate against thepolishing pad during polishing of the substrate; and (c) a retainingring rotatable coupled to the spindle and adapted to surround thesubstrate being pressed against the polishing pad during polishing andto limit lateral movement of the substrate relative to the polishinghead. The method includes rotating the spindle and membrane of thepolishing head at a first rotation rate during polishing; and rotatingthe retaining ring of the polishing head at a second rotation rateduring polishing so as to cause the substrate to rotate relative to themembrane of the polishing head.

In some aspects, a method of polishing a substrate is provided thatincludes pressing the substrate against a polishing pad using apolishing head having (a) a rotatable spindle; (b) a membrane coupled tothe rotatable spindle and adapted to press the substrate against thepolishing pad during polishing of the substrate; (c) a retaining ringcoupled to the spindle and adapted to surround the substrate beingpressed against the polishing pad during polishing and to limit lateralmovement of the substrate relative to the polishing head; and (d) atleast one rotation mechanism coupled to the retaining ring, adapted tocontact the substrate during polishing and adapted to allow thesubstrate to rotate at a different rate than the spindle during theduring polishing. The method includes rotating the spindle and membraneof the polishing head at a first rotation rate during polishing; androtating the at least one rotation mechanism coupled to the retainingring of the polishing head at a second rotation rate during polishing soas to cause the substrate to rotate relative to the membrane of thepolishing head.

Numerous other aspects are provided. Other features and aspects of thepresent invention will become more fully apparent from the followingdetailed description, the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram depicting a side view of an examplechemical-mechanical planarization system for polishing substratesaccording to embodiments of the present invention.

FIGS. 2A-2B are top schematic views of a substrate and retaining ringduring polishing in accordance with embodiments of the presentinvention.

FIG. 3 is a schematic side view of a first embodiment of an examplepolishing system provided in accordance with the present invention.

FIG. 4A is a schematic side view of a second embodiment of an examplepolishing system provided in accordance with the present invention.

FIGS. 4B-4E are schematic top views of example embodiments of thepolishing system of FIG. 4A in accordance with the present invention.

DETAILED DESCRIPTION

The present invention provides methods and apparatus for improvinguniformity during chemical mechanical polishing of large substrates(e.g., semiconductor wafers, glass substrates used for liquid crystaldisplays (LCDs) or solar cells, or any other similar underlying and/orsupporting layer/structure).

As stated, during CMP a substrate is placed face down on a polishing padand pressed against, and rotated relative to, the polishing pad via apolishing head. A slurry containing abrasive particles and/or chemicalsmay be supplied to the polishing pad to assist in material removal fromthe substrate as the substrate is pressed against and rotated relativeto the polishing pad. In this manner, the top surface of the substratemay be planarized.

FIG. 1 illustrates a side view of an example chemical-mechanicalplanarization (CMP) system 100 for polishing substrates in accordancewith the present invention. The system 100 includes a load cup assembly102 for receiving a substrate (not shown in FIG. 1) to be polished andfor holding the substrate in place for a polishing head 104 to pick up.The polishing head 104 is supported by an arm 106 that is operative tomove the head 104 between the load cup assembly 102 and a polishing pad108 on a rotating platen 110. In operation, the polishing head 104 picksup the substrate from the load cup assembly 102 and carries it to thepolishing pad 108. As the polishing pad 108 is rotated on the platen110, the head 104 rotates and pushes the substrate down against thepolishing pad 108. For example, an expandable membrane (not shown)within the polishing head 104 may contact and press the substrateagainst the polishing pad 108. Note that in the embodiment shown, thediameter of the polishing pad 108 is more than twice that of thesubstrate. Other platen, polishing pad and/or substrate sizes may beused.

With reference to FIGS. 2A-2B, to maintain a substrate 202 in positionunder a polishing head 104, the polishing head 104 includes a retainingring 204 that surrounds the substrate 202 and limits its lateralmovement during polishing. The substrate 202 has a slightly smallerdiameter D₁ than a diameter D₂ of the retaining ring 204 (forming a gap206 between the substrate 202 and retaining ring 204 which isexaggerated in FIGS. 2A-2B). In some embodiments, the gap 206 may beabout 0.01 inches, although other gap sizes may be used.

Rotation of the polishing pad 108 during polishing generates a forcethat presses the substrate 202 against the retaining ring 204 as shownin FIG. 2B (causing the center of rotation of the substrate 202 to nolonger align with the center of rotation of the polishing head104/retaining ring 204). As mentioned, the polishing head 104 is rotatedduring polishing, which causes the retaining ring 204 to similarlyrotate. This rotation of the retaining ring 204 causes rotation(precession) of the substrate 202 in a manner similar to a gear wheeldue to the misalignment of the centers of rotation of the substrate 202and retaining ring 204. (Note that the membrane of the polishing head104 used to press the substrate 202 against the polishing pad 108typically has a low coefficient of friction, allowing the substrate 202to rotate relative to the membrane of the polishing head 104 duringpolishing.)

Due to alignment and/or tolerances within the polishing head 104, thepolishing head 104 may generate a non-concentric pressure profile as itpresses the substrate 202 against the polishing pad 108. Such anon-concentric pressure profile may produce a non-concentric and/orasymmetrical polish profile on the substrate 202, and is thusundesirable. However, rotation (precession) of the substrate 202relative to the polishing head 104 during polishing, as described above,may alleviate the affects of the non-concentric pressure profileproduced by the polishing head 104. For example, for a 300 mm substrate,the mismatch between the diameter of the substrate 202 and the retainingring 204 is typically large enough to allow the substrate 202 to precessabout 180 degrees or more relative to the polishing head 104 duringpolishing. This is generally sufficient to reduce and/or mask anyasymmetric polishing profile that might otherwise result from apolishing head's non-concentric pressure profile. However, anyasymmetric polishing profile is undesirable. Furthermore, for largersubstrate sizes such as 450 mm substrates, asymmetric polishing profilesmay be more pronounced. For example, the amount a substrate precessesrelative to the retaining ring 204 is proportional to the gap betweenthe substrate and retaining ring divided by the diameter of thesubstrate:

amount of precession˜(D ₂ −D ₁)/D ₁=(gap 206)/D₁

Accordingly, if the gap 206 remains relatively constant as substratesize is increased, the amount the substrate 202 precesses duringpolishing is reduced. This reduced precession may be insufficient tomask the asymmetric polishing profile resulting from a non-concentricpolishing head pressure profile.

In accordance with embodiments of the present invention, a polishinghead/retaining ring configuration is employed that allows active controlover the amount a substrate precesses during polishing. Such “activeprecession” allows a substrate to precess sufficiently to reduce and/orminimize the asymmetric polishing profile resulting from anon-concentric polishing head pressure profile. This is beneficial tosubstrates of any size (e.g., 200 mm, 300 mm, 450 mm or other sizedsemiconductor wafers, or any other substrate type or size).

FIG. 3 is a schematic side view of a first embodiment of an examplepolishing system 300 provided in accordance with the present invention.With reference to FIG. 3, the polishing system 300 includes polishinghead 104 coupled to a controller 302. The controller 302 may be acomputer, a microcontroller, a programmable logic controller or anyother suitable controller.

Polishing head 104 includes a central spindle 304 rotatably coupled to aretaining ring 204 via one or more bearing assemblies 306. A membrane308 is coupled to the central spindle 304 and may contact substrate 202,pressing substrate 202 against polishing pad 108. The membrane 308 isadapted to expand to press the substrate 202 against the polishing pad108. For example, the membrane 308 may be a liquid or gas filledbladder. In some embodiments, the portion of the membrane 308 thatcontacts the substrate 202 may be a low friction material such aspolytetrafluoroethylene (PTFE) or a similar material.

Spindle 304 is coupled to a first drive mechanism 310 and retaining ring204 is coupled to a second drive mechanism 312 to allow the spindle 304and retaining ring 204 to be driven at different rotation rates. In someembodiments, a single drive mechanism may be used through suitablegearing and/or belts to cause spindle 304 and retaining ring 204 torotate at different rates. Any suitable drive mechanisms may be usedsuch as one or more motors. Controller 302 may include computer programcode for directing rotation of spindle 304 and/or retaining ring 204during polishing as described further below.

Bearing assembly 306 keeps retaining ring 204 concentric with membrane308 and may comprise any suitable bearing assembly such as ballbearings, roller bearings, slide bearings, track bearings, non-contactbearings, or the like. The components of the bearing assembly 306, suchas the balls and races, may be formed of a material compatible with thechemistry used during chemical mechanical polishing within the polishingsystem 300 so as not to degrade rapidly or generate particles that couldcontaminate a substrate being polished. For instance, the bearingassembly 306 may be formed of a suitable polymer material. Alternativelyor additionally, the bearing assembly 306 may be shielded, sealed orotherwise isolated from the polishing chemistry.

In operation, substrate 202 is placed on the polishing pad 108 and ispressed against the polishing pad 108 by polishing head 104 (viaexpansion of membrane 308). Retaining ring 204 surrounds substrate 202within the polishing head 104, and also contacts polishing pad 108. Notethat a suitable abrasive slurry (not shown) may be applied to thepolishing pad 108 before and/or during polishing of the substrate 202.

Controller 302 causes drive 310 to rotate spindle 304 and membrane 308as indicated by arrow 314, and drive 312 to rotate retaining ring 204 asindicated by arrow 316. Polishing pad 108 is also rotated using the sameor a different drive mechanism under control of controller 302 oranother controller (not shown). As stated, rotation of polishing pad 108causes substrate 202 to slide into contact with retaining ring 204 asindicated by arrow 318.

In some embodiments, retaining ring 204 is rotated at a faster rate thanspindle 304. In other embodiments, retaining ring 204 is rotated at aslower rate than spindle 304. In either case, retaining ring 204 andspindle 304 rotate at different rates so that substrate 302 is activelyprecessed relative to membrane 308 (e.g., so that substrate 202 fullyrotates beneath membrane 308 during polishing).

In one or more embodiments, spindle 304 may be rotated at a rate ofabout 10 to about 150 rotations per minute (RPM), while retaining ring204 may be rotated at a rate of about 5 to about 300 RPM. For example,in some embodiments, retaining ring 204 may be rotated at about one-halfthe rotation rate of spindle 304, while in other embodiments, retainingring 204 may be rotated at about twice the rotation rate of spindle 304.Other rotation rates may be used for the spindle 304 and/or retainingring 204. Retaining ring 204 may be rotated during a portion of or theentire time spindle 304 is rotated, and/or may be maintained stationaryone or more times during polishing. Further, in some embodiments,retaining ring 204 may switch direction of rotation during polishing.

Polishing of substrate 202 continues until a desired amount of materialis removed from the substrate 202. Because retaining ring 204 rotates ata different rate than spindle 204, substrate 202 is actively precessedrelative to membrane 308 and non-concentric or otherwise asymmetricpolishing head pressure profile is averaged out during polishing (e.g.,producing a more uniform polish). This is beneficial to substrates ofany size (e.g., 200 mm, 300 mm, 450 mm or other sized semiconductorwafers, or any other substrate type or size).

FIG. 4A is a schematic side view of a second embodiment of an examplepolishing system 400 provided in accordance with the present invention.The polishing system 400 of FIG. 4A is similar to the polishing system300 of FIG. 3. However, in the polishing system 400 of FIG. 4A, theretaining ring 204 remains stationary during polishing as indicated bycoupling 402, and one or more rollers 404 are employed to rotatesubstrate 202 relative to membrane 308 during polishing. FIG. 4B is aschematic top view of the polishing system 400 showing two rollers 404 aand 404 b. It will be understood that other numbers of rollers may beused (e.g., 3, 4, 5, etc.).

Rollers 404 a and 404 b may be formed from any suitable material such aspolyphenylene sulfide (PPS), polyetheretherketone (PEEK), polyethyleneterephthalate (PET) or the like. Exemplary diameters for the rollers 404a-b may range from about 0.5 to about 2 inches. In some embodiments, therollers 404 a-b may be spaced apart by about 1 to 5 inches. Othermaterials, sizes and/or spacings may be used for the rollers.

Controller 302 causes drive 310 to rotate spindle 304 and membrane 308as indicated by arrow 314, and drive 312 to rotate rollers 404 a and 404b as indicated by arrow 416. In some embodiments a single drivemechanism may be used to rotate spindle 304, roller 404 a and/or roller404 b through use of appropriate belts, gears or the like; or a separatedrive mechanism may be used as shown in FIG. 4A. Polishing pad 108 isalso rotated using the same or a different drive mechanism under controlof controller 302 or another controller (not shown). Rotation ofpolishing pad 108 causes substrate 202 to slide into contact withrollers 404 a and 404 b as indicated by arrow 418. This region may bereferred to as the trailing edge of the retaining ring 204, while theopposite side may be referred to as the leading edge of the retainingring 204.

In some embodiments, rollers 404 a and 404 b are rotated at a fasterrate than spindle 304. In other embodiments, rollers 404 a and 404 b arerotated at a slower rate than spindle 304. In either case, rollers 404a-b and spindle 304 rotate at different rates so that substrate 302 isactively precessed relative to membrane 308 (e.g., so that substrate 202fully rotates beneath membrane 308 during polishing).

In one or more embodiments, spindle 304 may be rotated at a rate ofabout 10 to about 150 rotations per minute (RPM), while rollers 404 a-bmay be rotated at a rate of about 30 to about 3600 RPM (depending on thediameter of the rollers). For example, in some embodiments, rollers 404a-b may be rotated so that substrate 202 rotates at about one-half therotation rate of spindle 304, while in other embodiments, rollers 404a-b may be rotated so that substrate 202 rotates at about twice therotation rate of spindle 304. Other rotation rates may be used for thespindle 304 and/or rollers 404 a-b. Rollers 404 a-b may be rotatedduring a portion of or the entire time spindle 304 is rotated, and/ormay be maintained stationary one or more times during polishing.Further, in some embodiments, rollers 404 a-b may switch direction ofrotation during polishing.

Polishing of substrate 202 continues until a desired amount of materialis removed from the substrate 202. Because rollers 404 a-b rotate at adifferent rate than spindle 204, substrate 202 is actively precessedrelative to membrane 308 and any non-concentric or otherwise asymmetricpolishing head pressure profile is averaged out during polishing (e.g.,producing a more uniform polish). This is beneficial to substrates ofany size (e.g., 200 mm, 300 mm, 450 mm or other sized semiconductorwafers, or any other substrate type or size).

In general, retaining ring 204 may be formed from any suitable materialsuch as polyphenylene sulfide (PPS), polyetheretherketone (PEEK),polyethylene terephthalate (PET) or the like. In embodiments in whichrollers 404 are employed, such as in FIGS. 4A-4C, the retaining ring 204may be modified to improve substrate edge polish behavior. For example,features used to allow entry of slurry into the polishing head 104 maybe modified depending on the application. In some embodiments, it may bedesirable to have slurry build up during polishing so additional slurrygrooves may be provided along the leading edge of the retaining ring 204relative to the trailing edge of the retaining ring 204 (near rollers404 a-b). Likewise, in some embodiments it may be desirable to havelittle slurry build up during polishing, so more slurry grooves may beprovided along the trailing edge of the retaining ring 204 (near rollers404 a-b) than along the leading edge of the retaining ring 204.Similarly, different forces may be applied along the trailing edge ofthe retaining ring 204 relative to the leading edge of the retainingring 204 to better control pad rebound during polishing. Similarly, theretaining ring 204 may have different geometries (e.g., widths) alongthe trailing and leading edges of the retaining ring 204.

While retaining ring 204 is shown as being a single ring section, itwill be understood that retaining ring 204 may comprise multiple ringsections as illustrated by ring sections 204 a and 204 b in FIG. 4C.More than two ring sections may be used, as may inner or outer ringsections. FIG. 4D illustrates a retaining ring 204 having larger and/ormore slurry grooves 420 a along a leading edge of the retaining ring 204than slurry grooves 420 b along the trailing edge of the retaining ring204. Such an arrangement may be reversed if desired. FIG. 4E illustratesa retaining ring 204 that is wider along a leading edge of the retainingring 204 than along a trailing edge of the retaining ring 204. Such anarrangement may be reversed if desired.

Accordingly, while the present invention has been disclosed inconnection with example embodiments thereof, it should be understoodthat other embodiments may fall within the spirit and scope of theinvention, as defined by the following claims.

The invention claims is:
 1. A chemical mechanical polishing apparatuscomprising: a polishing head comprising: a rotatable spindle; a membranecoupled to the rotatable spindle and adapted to press a substrateagainst a polishing pad during polishing of the substrate; and aretaining ring rotatable coupled to the spindle and adapted to surrounda substrate being pressed against a polishing pad during polishing andto limit lateral movement of the substrate relative to the polishinghead; and a drive mechanism coupled to the retaining ring and adapted todrive the retaining ring at a different rate of rotation than thespindle during polishing.
 2. The chemical mechanical polishing apparatusof claim 1 further comprising a controller adapted to cause the drivemechanism to rotate the retaining ring at a different rate of rotationthan the spindle during polishing.
 3. The chemical mechanical polishingapparatus of claim 2 wherein the controller is adapted to cause thedrive mechanism to rotate the retaining ring at about twice the rate ofrotation of the spindle during polishing.
 4. The chemical mechanicalpolishing apparatus of claim 2 wherein the controller is adapted tocause the drive mechanism to rotate the retaining ring at about one-halfthe rate of rotation of the spindle during polishing.
 5. A method ofpolishing a substrate comprising: pressing the substrate against apolishing pad using a polishing head having: a rotatable spindle; amembrane coupled to the rotatable spindle and adapted to press thesubstrate against the polishing pad during polishing of the substrate;and a retaining ring coupled to the spindle and adapted to surround thesubstrate being pressed against the polishing pad during polishing andto limit lateral movement of the substrate relative to the polishinghead; rotating the spindle and membrane of the polishing head at a firstrotation rate during polishing; and rotating the retaining ring of thepolishing head at a second rotation rate during polishing so as to causethe substrate to rotate relative to the membrane of the polishing head.6. The method of claim 5 wherein the first rate is less than the secondrate.
 7. The method of claim 5 wherein the first rate is greater thanthe second rate.
 8. A chemical mechanical polishing apparatuscomprising: a polishing head comprising: a rotatable spindle; a membranecoupled to the rotatable spindle and adapted to press a substrateagainst a polishing pad during polishing of the substrate; a retainingring rotatable coupled to the spindle and adapted to surround asubstrate being pressed against a polishing pad during polishing and tolimit lateral movement of the substrate relative to the polishing head;and at least one rotation mechanism coupled to the retaining ring,adapted to contact a substrate during polishing and adapted to allow thesubstrate to rotate at a different rate than the spindle during theduring polishing.
 9. The chemical mechanical polishing apparatus ofclaim 8 wherein the at least one rotation mechanism comprises at leastone roller rotatably coupled to a trailing edge of the retaining ring.10. The chemical mechanical polishing apparatus of claim 8 wherein theretaining ring is stationary during polishing.
 11. The chemicalmechanical polishing apparatus of claim 8 wherein the retaining ringcomprises multiple retaining ring sections.
 12. The chemical mechanicalpolishing apparatus of claim 8 wherein the retaining ring has adifferent number of slurry grooves along a leading edge of the retainingring than along a trailing edge of the retaining ring.
 13. The chemicalmechanical polishing apparatus of claim 8 wherein the retaining ring hasa different width along a leading edge of the retaining ring than alonga trailing edge of the retaining ring.
 14. A method of polishing asubstrate comprising: pressing the substrate against a polishing padusing a polishing head having: a rotatable spindle; a membrane coupledto the rotatable spindle and adapted to press the substrate against thepolishing pad during polishing of the substrate; a retaining ringcoupled to the spindle and adapted to surround the substrate beingpressed against the polishing pad during polishing and to limit lateralmovement of the substrate relative to the polishing head; and at leastone rotation mechanism coupled to the retaining ring, adapted to contactthe substrate during polishing and adapted to allow the substrate torotate at a different rate than the spindle during the during polishing;rotating the spindle and membrane of the polishing head at a firstrotation rate during polishing; and rotating the at least one rotationmechanism coupled to the retaining ring of the polishing head at asecond rotation rate during polishing so as to cause the substrate torotate relative to the membrane of the polishing head.
 15. The method ofclaim 14 wherein the at least one rotation mechanism comprises at leastone roller rotatably coupled to a trailing edge of the retaining ring.16. The method of claim 14 wherein the retaining ring is stationaryduring polishing.
 17. The method of claim 14 wherein the retaining ringcomprises multiple retaining ring sections.
 18. The method of claim 14wherein the retaining ring has a different number of slurry groovesalong a leading edge of the retaining ring than along a trailing edge ofthe retaining ring.
 19. The method of claim 14 wherein the retainingring has a different width along a leading edge of the retaining ringthan along a trailing edge of the retaining ring.
 20. The method ofclaim 14 further comprising applying a different pressure along aleading edge of the retaining ring than along a trailing edge of theretaining ring during polishing.